1. Field of the Invention
The present invention generally relates to a methods and system for radiation therapy treatment planning, more specifically to an improved method and system that reduces variations in the planning of radiation therapy treatment.
2. Description of the Related Art
Image-guided three-dimensional (3-D) radiotherapy aims at delivering the largest possible and the most homogeneous radiation dose to a tumor target while keeping the dose to surrounding normal tissues to a minimum. Thus, the prime step in radiotherapy planning is to determine and to delineate a target volume in three dimensions in order to produce a treatment volume which will encompass the tumor (and normal tissues) with as much precision as possible.
The routine use of 3-D treatment planning in curative radiation therapy and the growing implementation of intensity-modulated radiotherapy (IMRT) or proton treatment in many centers require a very accurate knowledge of the volumes to be treated, with a good reproducibility, not only within same physician at different period of time but also between physicians of varying geographic practices and locations. Older techniques used larger and unshaped fields, and this has led to either a limitation of the total dose with many treatment failures, or to an excessive rate of complications. Conversely, new technologies, such as IMRT or proton, if not associated with an extremely careful definition of the target, may lead to an excess of geographic misses and local failures. The International Commission on Radiation Units and Measurements (ICRU) Reports 50 and 62, published in 1993 and 1999, have provided a formal definition to describe volumes in radiation planning. In brief, the gross tumor volume (GTV) is the gross extent of the malignancy. The clinical target volume (CTV) is the GTV plus a margin to include local subclinical tumor spread. The CTV can also include regional nodes. The GTV and CTV are based on anatomic, biological and clinical considerations and do not account for the technical factors of treatment. The planning target volume (PTV) is the CTV plus a margin to ensure that the CTV receives the prescribed dose. Previous studies have shown that large discrepancies were found when different physicians were asked to delineate volumes in the same patient. These discrepancies are worrisome when considering the high precision achieved with conformal therapy and even more with IMRT. It has been stated that inadequate definition of the GTV/CTV leads to a systematic geographic miss of the tumor and that, for some locations, these inconsistencies may dominate all other errors in radiotherapy planning and delivery. A recent study revealed the following:    (1) variation in knowledge and/or interpretation in the basic ICRU definitions;    (2) variation in understanding and/or concept for microscopic tumor extent (CTV);    (3) variation between the theoretical knowledge (stated region of interest) and the practice (drawn region of interest).
Therefore, measures that are able to decrease discrepancies and improve inter-user discrepancy will have a significant clinical impact on the success of curing cancer.